Plant Physiology - Short Questions (2-3 Marks)- short questions - Biology

 

Question: Define water potential. What are its two main components?

Answer: Water potential (Ψ w ) is the potential energy of water per unit volume relative to pure water in reference conditions. It represents the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects such as surface tension. Its two main components are:

 

Solute potential (Ψ s ): A measure of the effect of dissolved solutes on water potential. It is always negative or zero.

 

Pressure potential (Ψ p): A measure of the pressure exerted on water (e.g., turgor pressure). It is usually positive.

 

Question: Differentiate between diffusion and facilitated diffusion.

Answer:

 

Diffusion: Passive movement of substances from a region of higher concentration to a region of lower concentration, down the concentration gradient, directly through the lipid bilayer (for small, nonpolar molecules) or through channels. It does not require carrier proteins.

 

Facilitated Diffusion: Passive movement of substances from a region of higher concentration to a region of lower concentration, down the concentration gradient, but requiring the help of specific membrane proteins (channels or carriers). It does not require metabolic energy.

 

Question: What is plasmolysis? Describe what happens to a plant cell during plasmolysis.

Answer: Plasmolysis is the process in which the protoplast (cell membrane and cell contents) of a plant cell shrinks away from the cell wall when the cell is placed in a hypertonic solution. During plasmolysis, water moves out of the cell by osmosis, causing the protoplast to contract and pull away from the rigid cell wall. This leads to the loss of turgor and wilting of the plant.

 

Question: Explain the phenomenon of guttation. From where does water get released during guttation?

Answer: Guttation is the exudation of water droplets from the edges or tips of leaves of some vascular plants, especially in the early morning. This occurs when root pressure is high and transpiration is low. Water gets released from specialized pores called hydathodes, which are present at the tips of leaf veins.

 

Question: Briefly explain the role of root pressure in water transport.

Answer: Root pressure is the positive pressure that develops in the xylem sap of roots due to the active absorption of mineral ions by root cells, which then creates a water potential gradient, causing water to move into the xylem by osmosis. This pressure can push water up a short distance (up to a few meters) in the xylem. It is more noticeable during periods of low transpiration, such as at night.

 

Question: How does the opening of stomata occur?

Answer: The opening of stomata is primarily regulated by the turgidity of the guard cells. When guard cells absorb water (e.g., due to K+ ion influx followed by water entry by osmosis), they become turgid. The inner walls of the guard cells are thicker and inelastic, while the outer walls are thinner and elastic. This differential thickening causes the guard cells to bow outwards, creating an opening (stomatal aperture) between them.

 

Question: What is the significance of the Apoplast pathway in water movement?

Answer: The Apoplast pathway is the system of adjacent cell walls that is continuous throughout the plant, extending from the root hairs to the xylem. It allows for the rapid, bulk flow of water and solutes through the non-living parts of the plant (cell walls and intercellular spaces) without crossing any cell membranes, except at the endodermis (due to Casparian strips). It is a major pathway for water transport, especially in the cortex of the root.

 

Question: Define mass flow hypothesis in terms of food transport in plants.

Answer: The Mass Flow Hypothesis (also known as the Pressure Flow Hypothesis) explains the translocation of sugars (food) through the phloem. It states that sugars are actively loaded into sieve tube elements at the source (e.g., leaves where photosynthesis occurs), creating a high turgor pressure. This pressure drives the bulk flow of the sugar solution through the sieve tubes towards areas of lower pressure (sinks, e.g., roots, fruits, growing points) where sugars are unloaded.

 

Question: What is the function of the electron transport system (ETS) in cellular respiration?

Answer: The electron transport system (ETS), located on the inner mitochondrial membrane in eukaryotes, is the final stage of aerobic respiration. Its function is to transfer electrons from NADH and FADH2 (produced during glycolysis and Krebs cycle) through a series of protein complexes. This electron flow generates a proton gradient across the inner membrane, which is then used by ATP synthase to produce a large number of ATP molecules through oxidative phosphorylation.

 

Question: What is fermentation? Name the two common types of fermentation.

Answer: Fermentation is an anaerobic process (occurs in the absence of oxygen) that involves the incomplete breakdown of glucose to generate ATP. It regenerates NAD+ from NADH, allowing glycolysis to continue. The two common types are:

 

Lactic acid fermentation: Pyruvic acid is converted to lactic acid (e.g., in muscle cells during strenuous exercise).

 

Alcoholic fermentation: Pyruvic acid is converted to ethanol and carbon dioxide (e.g., in yeast).

 

Question: What is a respiratory quotient (RQ)? How is it calculated?

Answer: The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide (CO2) evolved to the volume of oxygen (O2) consumed during respiration. It is calculated as:

RQ = Volume of CO2 evolved / Volume of O2 consumed

It indicates the type of respiratory substrate being utilized (e.g., 1.0 for carbohydrates, <1 for fats and proteins).

 

Question: Briefly describe why the Krebs cycle is considered an amphibolic pathway.

Answer: The Krebs cycle (Citric Acid Cycle) is considered an amphibolic pathway because it serves both catabolic and anabolic functions.

 

Catabolic: It breaks down acetyl CoA, releasing CO2 and generating ATP, NADH, and FADH2.

 

Anabolic: It provides intermediates (e.g., α-ketoglutarate, oxaloacetate, succinyl CoA) that are used as precursors for the synthesis of various biomolecules like amino acids, chlorophyll, and fatty acids.

 

Question: What is seed dormancy? Mention two ways by which it can be broken naturally.

Answer: Seed dormancy is a state in which a viable seed fails to germinate even under favorable environmental conditions (adequate moisture, temperature, oxygen). It is caused by internal factors (e.g., impermeable seed coat, immature embryo, presence of inhibitors).

Two natural ways to break dormancy are:

 

Scarification: Mechanical or chemical weakening of a hard seed coat to allow water and oxygen uptake (e.g., by microbial action or passage through animal digestive tracts).

 

Stratification: Exposure to a period of low temperature, which is often required to break dormancy in seeds of temperate plants.

 

Question: What is vernalization? What is its significance?

Answer: Vernalization is the process by which certain plants require a period of low temperature (chilling treatment) to induce or accelerate flowering. Its significance is:

 

It prevents premature flowering in temperate regions, ensuring that flowering occurs only after the cold season, when conditions are more favorable for growth and reproduction.

 

It helps synchronize flowering with the appropriate growing season.

 

Question: Name any two physiological effects of Auxins in plants.

Answer: Two physiological effects of Auxins are:

 

Cell elongation: Promotes elongation of cells, especially in shoots, leading to growth.

 

Apical dominance: Inhibits the growth of lateral (axillary) buds, leading to the preferential growth of the apical bud. (Other effects: root initiation, fruit development, preventing abscission).

 

Question: Mention two applications of Gibberellins in agriculture.

Answer: Two applications of Gibberellins in agriculture are:

 

Increasing fruit size: Promotes the size of fruits like apples and grapes.

 

Delaying senescence: Delays the aging of fruits and allows them to be stored for longer periods. (Other applications: bolting in rosette plants, speeding up malting in brewing industry).

 

Question: What is the primary role of Cytokinins in plants?

Answer: The primary role of Cytokinins is to promote cell division (cytokinesis). They also play a crucial role in:

 

Overcoming apical dominance.

 

Promoting lateral shoot growth.

 

Delaying leaf senescence (aging).

 

Regulating nutrient mobilization.

 

Question: Explain the concept of differentiation in plant growth.

Answer: Differentiation in plant growth is the process by which cells originating from meristems (primary and secondary) undergo changes in their structure and function to become specialized for specific roles. For example, meristematic cells differentiate into xylem vessels, phloem sieve tubes, epidermal cells, or parenchyma cells, each with a distinct morphology and function.

 

Question: Name the plant growth regulator known as the 'stress hormone'. Why is it called so?

Answer: Abscisic Acid (ABA) is known as the 'stress hormone'. It is called so because its synthesis increases significantly in response to various environmental stresses, such as drought, high salinity, and cold. ABA helps plants cope with these stresses by inducing adaptive responses like:

 

Promoting stomatal closure to reduce water loss during drought.

 

Inducing seed dormancy to ensure survival under unfavorable conditions.

 

Question: Differentiate between long-day plants and short-day plants regarding their flowering response.

Answer:

 

Long-day plants (LDPs): Require exposure to a light period (photoperiod) that is longer than a critical duration to initiate flowering. They typically flower in late spring or early summer. (e.g., wheat, spinach).

 

Short-day plants (SDPs): Require exposure to a light period (photoperiod) that is shorter than a critical duration to initiate flowering. They typically flower in late summer or autumn. (e.g., Xanthium, tobacco).